In semiconductor fabrication, in particular, structures having a large ratio between the depth measured perpendicular to the surface of a substrate and the lateral dimensions (HAR structures, HAR=high aspect ratio) are increasingly being produced and used, for example for capacitors in memory cells of memory components. Structures of this type have to be characterized at least on the basis of random sampling in the course of production, their dimensions, in particular, being determined in order to monitor the production line and, if appropriate, to track process parameters. This characterization is conventionally done for example by breaking the semiconductor substrate, a structure arranged at the edge of the break subsequently being imaged by scanning electron microscopy, scanning force microscopy or in some other suitable way in order to characterize it and, in particular, to determine its dimensions from the imaging. Principally in the case of laterally small structures, the substrate must contain a multiplicity thereof in order that at least one is situated at the edge of the break. The breaking of the wafer generally precludes further processing thereof.
In an alternative method, a cutout serving as a viewing window is produced in the substrate by means of a focused ion beam, which cutout incipiently cuts the depth structure. The cutout is arranged and formed in such a way that the incipiently cut structure can subsequently be detected or imaged by scanning electron microscopy by means of an electron beam that is obliquely incident on the incipiently cut structure.
What is problematic about this method is the so-called “waterfall effect”, which stems from the unavoidable expansion of the focused ion beam and results in the incipiently cut structure being altered while it is actually being incipiently cut. The waterfall effect can be minimized or avoided in the case of a simple structure by prior deposition of a protection cap. For HAR structures, however, there is no conventional method for avoiding the waterfall effect.